EHN: pending_files tests for user-modified runtime params

The procedure for determining whether a user has modified the
runtime params of a processing job and wants to re-submit the job
is very rudimentary:

- A user modifies one or more .ini files from one of the .meegpipe
  reports.

- After the user is done modifying runtime params, she deletes the
  symbolic link corresponding to the edited .meegpipe directory.

- batman.pending_files realizes that the symbolic link of file X is
  newer than X.meegpipe, indicating that the user has manually
  deleted the link (indicating that she wants to re-reprocess the
  file).